A stoat (or a short tailed weasel) is a small mammal of the family Mustelidae. Males are bigger than females. Stoats in their white winter coat are also called ermines. They can grow to be as long as 30 centimeters (a foot long). They eat other small animals and bird eggs, and can kill animals bigger than themselves. They can also store food for later. They kill by biting the neck of their prey at the place where the skull attaches to the rest of the body.

Stoats are long and thin with short legs, small ears, and thick warm fur. Their fur is brown, but changes to white in the winter. The tail has a black tip all year round. Stoats have a good sense of smell, and they talk and hunt using smell. They do not see color as well as humans, but they can see better at night. Stoats are not nocturnal, and are most active during dawn and dusk. Like skunks, stoats can spray a bad smelling fluid when they are scared. They are also good at climbing trees.

Stoats live alone and are territorial. They mate once a year and have several babies, which are called kits. The kits may not develop for 8-9 months after the female becomes pregnant. When weather conditions are good and there is plenty of food, the kits begin to grow and are born within a month. The males do not help raise the babies.